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 * modification, are permitted provided that the following conditions are
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 * in the documentation and/or other materials provided with the
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package io.grpc.examples.header;

import io.grpc.ForwardingServerCall.SimpleForwardingServerCall;
import io.grpc.Metadata;
import io.grpc.ServerCall;
import io.grpc.ServerCallHandler;
import io.grpc.ServerInterceptor;
import io.grpc.Status;

import java.util.logging.Logger;

/**
 * A interceptor to handle server header.
 */
public class HeaderServerInterceptor implements ServerInterceptor {

  private static final Logger logger = Logger.getLogger(HeaderServerInterceptor.class.getName());

  private static Metadata.Key<String> customHeadKey =
      Metadata.Key.of("custom_server_header_key", Metadata.ASCII_STRING_MARSHALLER);


  @Override
  public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
      String method,
      ServerCall<RespT> call,
      final Metadata.Headers requestHeaders,
      ServerCallHandler<ReqT, RespT> next) {
    logger.info("header received from client:" + requestHeaders.toString());
    return next.startCall(method, new SimpleForwardingServerCall<RespT>(call) {
      boolean sentHeaders = false;

      @Override
      public void sendHeaders(Metadata.Headers responseHeaders) {
        responseHeaders.put(customHeadKey, "customRespondValue");
        super.sendHeaders(responseHeaders);
        sentHeaders = true;
      }

      @Override
      public void sendPayload(RespT payload) {
        if (!sentHeaders) {
          sendHeaders(new Metadata.Headers());
        }
        super.sendPayload(payload);
      }

      @Override
      public void close(Status status, Metadata.Trailers trailers) {
        super.close(status, trailers);
      }
    }, requestHeaders);
  }
}
